Essentially all modern medical scanners export data in this format.

This fantastic site will let you view (after upload) DICOM images in a web browser:

http://slicedrop.com/

There are a number of accessible (ie not clinical radiology priced) viewers available, the best of the lot for general use being Osirix [1] (OS X only), and ClearCanvas [2] (Windows only). Ginkgo CADx [3] and Mint viewer [4] are also good, and both cross-platform.

There are several well-regard open-source libraries for DICOM: gdcm [5] and DCMTK [6]. Widely used open-source medical image visualization SDKs with DICOM support include MITK [7] and 3D Slicer [8] (the afore-mentioned ClearCanvas is also an SDK in some sense).

[edit: formatting and add link]

1. http://en.wikipedia.org/wiki/OsiriX

2. http://www.clearcanvas.ca/dnn/

3. http://ginkgo-cadx.com/en/

4. http://www.mint-medical.de/

5. http://en.wikipedia.org/wiki/GDCM

6. http://dicom.offis.de/dcmtk.php.en

7. http://www.mitk.org/

8. http://www.slicer.org